Web Worker support

[sguimmara]

Currently, AFAIK it is not possible to use copc.js with workers without some form of hack.

The most performance critical part seems to be the LAZ decompression (namely Las.PointData.decompressChunk()). This could very easily be done in a worker while keeping the API almost identical.

I could try to setup a rough PR for discussion if you'd like.

[connormanning]

I'm not quite sure what you mean - both viewer.copc.io and the Potree implementation for COPC/EPT use copc.js via web workers to decompress LAZ data without anything hacky going on.

Can you be more specific with exactly what you are trying to accomplish and what issue you are running into?

[sguimmara]

Can you be more specific with exactly what you are trying to accomplish and what issue you are running into?

I'm implementing COPC support for the web library Giro3D.

I would like to move the laz decompression part in a worker. The decompression occurs in Copc.loadPointDataBuffer(), but I don't see how I could inject the worker logic so that the Las.PointData.decompressChunk() happens in a worker.

[connormanning]

All of the functions here are part of the public API. If you'd like to pull them apart and run some of those parts in a web worker, you can do so. This library provides building blocks and utility functions (and also works in NodeJS), so putting implementation details of composable functions into web workers would probably be out of scope here.

For example, in Potree we pass a compressed LAZ buffer received from the fetch API into a worker, where we decompress it and create a View of it, and then extract the data into GL-compatible buffers.

If you specifically want Las.PointData.decompressChunk() to happen in a worker, with the goal of achieving the functionality of Copc.loadPointDataBuffer(), then you can see here that you can use the existing API to do something like this:

function mainThreadStuff() {
  // Here you would already have the COPC metadata, LAS header, node you wish to fetch, etc.
  const compressed = await Copc.loadCompressedPointDataBuffer(filename, node)
  someWorker.postMessage({ compressed, header, node }, [compressed])
}

// Worker code.
function decompress(event) {
  const { compressed, header, node } = event.data
  const { pointDataRecordFormat, pointDataRecordLength } = header
  const { pointCount } = node

  const decompressed = Las.PointData.decompressChunk(
    compressed,
    { pointCount, pointDataRecordFormat, pointDataRecordLength },
    lazPerf
  )
  postMessage(decompressed, [decompressed])
}

I just typed this up now as pseudo-code so do not expect it to work - but hopefully it demonstrates my point: that the building blocks you need to accomplish this via web worker are already part of the public API.

[sguimmara]

Thanks ! I'll try that and inform how it goes

[sguimmara]

loadCompressedPointDataBuffer() is not part of the public API AFAIK. It is not exported in the Copc object:

export const Copc = {
  create,
  loadHierarchyPage,
  loadPointDataBuffer,
  loadPointDataView,
}

That's why I couldn't "inject" my worker.

If it were part of the public API, that would be great :)

[connormanning]

That's true, it's such a light wrapper that I probably wasn't sure it was worth exposing - since it's just a range fetch. So a more accurate code sample would use your COPC getter:

  const { pointDataOffset, pointDataLength } = node
  const compressed = await get(pointDataOffset, pointDataOffset + pointDataLength)

But that can absolutely be added to the public API - no objections to that.

[connormanning]

Added, and published to npm as current latest version 0.0.7.

[sguimmara]

Thanks for your quick response !